It is known that in the dry or drying end section or portion of a paper making machine the moisture-bearing paper web is directed along a serpentine path in wrapping relation with drying cylinders or drums arranged in tiers and having the cylinders in one tier staggered with respect to the cylinders or drums in the other tier. The dryer drums are heated, as by steam, and the traveling paper web is urged against the heated drums as by a porous, air-permeable endless support band which may be a felt generally woven from cotton or a plastic wire fabric belt. Generally, each tier of drying cylinders has such a support band or felt associated therewith. That is, the upper support band or felt presses the paper web against the drying cylinders of the upper tier while the lower support band or felt presses the paper web against the drying cylinders of the lower tier. As is known in the art, the respective support bands run between pairs of drying cylinders over a deflecting means such as, for example, a guide roller. In its travel as from an upper to a lower situated drying cylinder, or vice-versa, the paper web runs freely, that is, without in any way being supported by one of the support bands. As a consequence of such an arrangement a pocket is created and defined as between the lengths of run-on and run-off of paper web (as between succeeding drying cylinders), the uncovered portion of a drying cylinder and the juxtaposed portion of the support band, of the other tier of drying cylinders, juxtaposed to said uncovered portion of said drying cylinder. As is known and as should be apparent, usually there are a plurality of such pockets in the drying end section of the paper making machine. The moisture evaporating from such run-on and run-off portions of the paper web collects within such pockets and creates a condition of high humidity therein and interferes with the maintenance of a desired drying temperature.
In the prior art, such moisture or vapor within the pockets is attempted to be removed therefrom as by causing the vapor to flow through the porous support belt or felt, or, generally laterally across and beyond the porous support felt and free running paper web.
U.S. Pat. No. 3,110,575 teaches the use of blast air blown through the support band or felt on one side of the related guide roll while, on the other side of such guide roll, a suction box is provided serving to receive vapors or moist air again passing out of the pocket and through the support band. In such an arrangement, of course, there is an attendant relatively high cost of construction and additional operating energy must be provided for the operation of the pumping means, for supplying the air blast, and for the operation of the suction boxes.
U.S. Pat. No. 3,427,727 discloses the use of an air blast box to provide air stream against and through the support band or felt. The air stream created is, in turn, peripherally contained or confined by a rectangular "air curtain" produced by a rectangular generally continuous slot or blow orifice. According to the patentee in said U.S. Pat. No. 3,427,727, the "air curtain" serves the purpose of permitting the blast of air to pass through the support band or felt with as little as possible attendant swirling of such air. However, a plurality of blow or air blast orifices 74--74 are provided in each of face of discharge plates 52 and 54 and such orifices 74 or more specifically, pairs of such orifices 74, within the blow zone between the box 28 and the support band, will create a plurality of respective swirl zones resulting in a loss of flow through the support band or felt. As a consequence high energy usage and losses are experienced in the creation of the air stream in the arrangement of said U.S. Pat. No. 3,427,727. Further, the box or apparatus 28 (of U.S. Pat. No. 3,427,727) supplies such air to both sides of the related guide roll 20. Consequently, the moisture laden air within the pocket can move out of such pocket only by moving laterally, with respect to such support band and paper web. This type of flow, in turn, causes the edges of the paper web to flutter (much as the free end of a flag in a strong wind) thereby increasing the danger of having the paper web tear.
The invention as herein disclosed and described is primarily directed to the solution of the foregoing as well as other related and attendant problems of the prior art.